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Full text of "Practical Organic Chemistry"

TYROSINE-LEUCINE                            133

PREPARATION 44.
Tyrosine, (OH).C0H4.CH.,.CH(NH,,).COOH
CH3X
Leucine,       ' >CH.CH.,CH(NH,).COOH
CM/
Beyer, Zcit., 1867, 436 ; E. Fischer, Bcr^ 1901, 34, 433,
100 grms. hoof or horn shavings (washed free from dirt).
2 5°    n      Oj6 c.c.) cone, sulphuric acid (in 750 c.c. water).
The shavings and acid are heated in around flask(\\litres) on
the water-bath until the greater part is dissolved, and then hoiled
with reflux condenser over wire-gauze for about 20 hours, until the
solution no longer gives the biuret reaction (p. 127). Add to a
little of the liquid two drops of copper sulphate solution and make
alkaline with caustic soda ; if the colouration is violet or pink
instead of blue, continue to boil. After boiling, the dark
coloured liquid is poured into a large basin and neutralised whilst
hot with slaked lime. The hot liquid is filtered and the residual
calcium sulphate replaced in the basin and extracted twice with
300 c.c. of hot water. The united filtrates are concentrated and
made up to a litre. The total quantity of oxalic acid (about 20
grams) required to precipitate the dissolved calcium salts is
determined by a preliminary estimation with 50 c.c. of the solution.
The liquid is boiled before adding the acid and filtered hot from
the precipitated calcium oxalate. The precipitate is extracted
twice with 250 c.c. of water and concentrated (to about 250 c.c,)
until crystals appear on the surface.
Tyrosilie.—On cooling, a brown, crystalline crust of impure
tyrosine separates. It is filtered, dissolved in the least quantity
of boiling water, boiled with a little animal charcoal, and
filtered. On cooling, long, white, silky needles of tyrosine arc
deposited. Yield about 2 grams.
Reactions.—Warm a small quantity of the substance with a
drop of strong nitric acid and add ammonia. A yellow solution
is produced in the first case, which changes to deep orange with
ammonia (xanthoproteic reaction). Warm with a solution o^
mercury in strong nitric acid (Millon's reagent). The liquid
turns red, and a red precipitate is tlien formed.
Leucine.—The filtrate from the tyrosine is further con-
ccntrcitecl on the w^tqr-bath to a small bulk, when on cooling a